Condensation plant for a steam turbine

ABSTRACT

A steam power plant consisting of high and low pressure turbine sections coupled together to drive a load such as an electric generator is provided with a composite condensing system which consists of a water-cooled main condenser connected to the steam discharge of the low pressure turbine section and an air-cooled auxiliary condenser connected to receive steam from the steam flow path intermediate the high and low pressure turbine sections. Steam flow to the auxiliary condenser can be controlled by valve means operated manually or automatically, as required, depending upon various limiting environmental parameters related to the available water supply for the main condenser.

United States Patent 1191 Schwarzenbach June 28, 1 974 4 gggggl PLANTFOR A STEAM FOREIGN PATENTS OR APPLICATIONS 380,170 ll/l9l8 Germany60/95 R [75] inventor: Alfred Schwarzenbach, Wettingen, 1,006,864 4/1957Germany 60/95 Switzerland 1731 51*. izzizzzzf ezrszfssi lme mute aSwltzer and Attorney, Agent, or Firm-Pierce, Scheffler & Parker [22]Filed: July 13, 1972 [21] Appl. No.: 271,419 [57] ABSTRACT A steam powerplant consisting of high and low pressure turbine sections coupledtogether to drive a load [30] Forelgn Pnomy Data such as an electricgenerator is provided with a com- Aug. 9, 1971 SWlIZCI'IaIICl ll708/7lposite condensing System consists of a water cooled main condenserconnected to the steam disfi F 'i charge of the low pressure turbinesection and an airl i 60 A 9 R cooled auxiliary condenser connected toreceive 1 o are 1 steam from the steam flow path intermediate the high56 R f ed and low pressure turbine sections. Steam flow to the 1 eerences It auxiliary condenser can be controlled by valve means UNITEDSTATES PATENTS operated manually or automatically, as required, de-1,741,605 12/1929 Baumann 60/95 R pending upon various limitingenvironmental parame- 1,782,220 11/1930 Wanamaker.... 60/95 R tersrelated to the available water supply for the main 2,l l 1,435 Munzingercondenser 3,l7l,258 3/l965 Caldwell 60/96 3,666,246 5/1972 Cohen 60/95 R4 Claims, 1 Drawing Figure PAmniomz 1914 3320.336

19 1 I a ,kJ 9

1 CONDENSATION PLANT FOR A STEAM TURBINE This invention relates to animprovement in the condensation system of a steam turbine plant whichfunctions to condense the steam after leaving the turbines for return tothe boiler to be again heated to vaporization and re-cycled through theturbines.

Every thermal power plant requires a heat sink to give up heat at thelower process temperature. Hitherto sufficient water from rivers, lakesor the sea has been available for this purpose in most industrializedcountries. As a result of antipollution measures, restrictions areincreasingly being imposed on the maximum permissible temperature riseof the water. In the summer months the water in many rivers is in shortsupply and, furthermore, the ambient temperature can be so high that thepermitted temperature rise in the water is quite small. Instead of arise of 12 C, for example, only 5 6 C may be acceptable in summer. Thepower station output must therefore be lowered accordingly, although thepower demand still remains very high because a great deal of electricityis used by air conditioning systems, especially in summer.

The known systems for condensing the steam are as follows: a. Surfacecondenser always supplied with fresh water, i.e., water drawn cold froma river, lake or sea. b. Surface condenser cooled by water which in turnis cooled by evaporation in a condenser. c. As (a), except that theheated water is cooled in a cooling tower before being discharged. d.Fixed-flow condenser, the condensate of which is cooled partly in a drycooling tower and then sprayed back into the condenser. e. Cooling towerwith direct heat exchange between steam and air.

So long as there is sufficient water available for 90 percent of theoperating time, solution (a) above is undoubtedly the most economical.In cases where there is an acute shortage of water throughout the year,one

of solutions (b) to (e) is unavoidable, although they are alleconomically inferior.

The objective of the present invention is, by employing additional,economically acceptable means, to produce the highest possible outputfrom steam turbine installations with water-cooled condensers at thosetimes when there is insufficient cooling water available, or thepermitted temperature rise of the cooling water is restricted.

This objective is achieved in that when the cooling capacity of the main(water) condenser is restricted, a partial flow of the working steam isdiverted from the turbine before expanding to condenser pressure and theheat to be removed from this steam to achieve condensation is given upto the ambient air.

A composite steam condensing system in accordance with the invention,i.e., one which is operative both with water and ambient air as thecooling mediums, comprises a conventional main, water-cooled condenserreceiving steam exhausted from the low pressure turbine unit and anauxiliary directly or indirectly air-cooled condenser to which steam issupplied by way of a branch pipe having a cut-off valve therein whichleads off the flow path of the steam through the turbine units at apoint prior to expansion of the steam to the pressure of the maincondenser, the steam condensed in the auxiliary air-cooled condenserbeing returned to the line connecting the outlet of the main,water-cooled condenser with the inlet to the boiler.

In an advantageous embodiment of the invention, the steam flow divertedfrom its main flow path to the auxiliary air-cooled condenser iscontrolled as a function of an operating characteristic of the mainwater-cooled condenser.

It is further beneficial, in accordance with the invention, if therespective flows of condensate from the main and auxiliary condensersmix at approximately the same temperature level.

A principal advantage of the composite condenser system according to theinvention lies particularly in the fact the air-cooled condenser systemis supplementary and is used only as needs require. Whereas before ithas been necessary to reduce the working steam flow rate because of thelimited cooling capacity of the main condenser, the full steam flow cannow be utilized up to the pressure at the point of diversion, while themain, water-cooled condenser receives only the permissible, reducedsteam flow. Beyond the branch point the diverted partial flow does nomore work, which is a loss thermodynamically and as regards efficiency,but the deciding factor is the power generated which, owing to theair-cooled auxiliary condenser, is in sum greater than without thiscondenser. The higher pressure in the auxiliary condenser also resultsin a higher temperature than that in the main condenser so that all theheat exchange surfaces are small and the costs-of the auxiliary system,which is used only for short periods, can be kept low.

The auxiliary, air-cooled condenser can be connected or disconnected byhand or by an automatic control system when, for example, the condenserpressure or the cooling-water discharge temperature exceeds a certainlimit. The condensate flows can be brought together immediately afterthe two condensers or at any other point, but it is of benefit if theymix at approximately the same temperature level because the flow fromthe auxiliary condenser is hotter and a thermodynamic loss is incurredif it is cooled by mixing with the cooler condensate stream.

A preferred embodiment of the invention is described in detail below andillustrated in the accompanying drawing, the single view of wyich is aschematic representation of a steam power plant equipped with anauxiliary air-cooled condenser of the mixed flow type.

With reference to the drawing, the steam power plant shown consistsessentially of the high and intermediatepressure section 1 and the lowpressure section 2 of the steam turbine, which together drive theelectrical generator 3. Steam leaving the low pressure section 2 iscondensed in the water-cooled main'condenser 4. The condensate fromcondenser 4 is conveyed by condensate pump 5 through pipe line 6 by wayof the bleeder steam-heated feedheaters 7, 8, 9 to the boiler (notshown) for reheating to produce steam for driving the turbines.

The interconnecting pipe 10 between the intermediate-pressure section 1and low pressure section 2 of the turbine incorporates a branch pipe 11which can be closed by valve 12. This branch pipe leads to auxiliarycondenser 13 which, in the example shown, is in the form of a mixed-flowcondenser. With the aid of a circulating pump 14 connected to the outletfrom the auxiliary condenser 13, a part of the condensate is withdrawnand fed through pipe 16 to cooling tower 17,

where it is cooled by air and then flows back into the auxiliarycondenser 13. g

The remainder of the condensate from the auxiliary condenser 13 isconveyed by return pump 18 in pipe line to the main condensate returnline 6. The two flows are best brought together at a junction point 19at which the condensate from the main condenser 14 has already beenheated to some extent by the feedheaters 7, 8, 9. In this way, mixing ofthe two condensate flows takes place at at least approximately the sametemperature level.

Valve 12 can be variable-setting.throttle valve, but it is cheaper, andwill in most cases be sufficient, to use a simple open/close valve.

I claim:

1. A steam turbine plant comprising steam turbine means receivingpressurized steam from a boiler, and a composite condensing system forthe steam comprising a main water-cooled condenser to which steam isdelivered after passing completely through said turbine means, a maincondensate return pipe line extending from said water-cooled condenserback to the boiler, an air-cooled auxiliary condenser, an auxiliary pipeline connected into the steam flow path through said turbine means at apoint prior to final expansion of the steam to the operating pressure ofsaid water-cooled condenser and which leads to said air-cooled auxiliarycondenser, controllable valve means located in said auxiliary pipe line,said valve means being opened. to divert a portion of the steam fromsaid turbine means for flow through said air-cooled auxiliary condenserin response to a reduction in the cooling capacity of said mainwater-cooled condenser below the normal value established for handlingthe total amount of steam normally passing through said turbine meansand an auxiliary condensate pipe line returning the condensate from saidair-cooled auxiliary condenser back to the boiler.

v2. A steam turbine plant as defined in claim 1 wherein the respectivecondensates from said main and auxiliary condensate pipe lines are mixedtogether at a point where they have substantially the same temperature.

3. A steam turbine plant as defined in claim 1 wherein said controllablevalve means located in said auxiliary pipe line connected into the steamflow path through said turbine means is constituted by a variablesetting throttle valve.

4. A steam turbine plant as defined in claim 1 wherein said controllablevalve means located in said auxiliary pipe line connected into the steamflow path through said turbine means is constituted by an openclosevalve.

1. A steam turbine plant comprising steam turbine means receivingpressurized steam from a boiler, and a composite condensing system forthe steam comprising a main water-cooled condenser to which steam isdelivered after passing completely through said turbine means, a maincondensate return pipe line extending from said water-cooled condenserback to the boiler, an air-cooled auxiliary condenser, an auxiliary pipeline connected into the steam flow path through said turbine means at apoint prior to final expansion of the steam to the operating pressure ofsaid water-cooled condenser and which leads to said air-cooled auxiliarycondenser, controllable valve means located in said auxiliary pipe line,said valve means being opened to divert a portion of the steam from saidturbine means for flow through said air-cooled auxiliary condenser inresponse to a reduction in the cooling capacity of said mainwater-cooled condenser below the normal value established for handlingthe total amount of steam normally passing through said turbine meansand an auxiliary condensate pipe line returning the condensate from saidair-cooled auxiliary condenser back to the boiler.
 2. A steam turbineplant as defined in claim 1 wherein the respective condensates from saidmain and auxiliary condensate pipe lines are mixed together at a pointwhere they have substantially the same temperature.
 3. A steam turbineplant as defined in claim 1 wherein said controllable valve meanslocated in said auxiliary pipe line connected into the steam flow paththrough said turbine means is constituted by a variable setting throttlevalve.
 4. A steam turbine plant as defined in claim 1 wherein saidcontrollable valve means located in said auxiliary pipe line connectedinto the steam flow path through said turbine means is constituted by anopen-close valve.